Laser radar methods and apparatus for measuring the velocity of moving objects with a laser transmitted beam are based on the premise that the frequency of the laser light backscattered from the object is subjected to a Doppler shift. The velocity of the irradiated object can be determined from the magnitude of this Doppler shift.
It is known to operate laser radar systems for measuring the velocity of moving objects either with a heterodyne system or a homodyne system.
Heterodyne and homodyne laser radar systems are described, for example, in the review article of Robert J. Keyes entitled "Heterodyne and nonheterodyne laser transceivers" published in the "Review of Scientific Instruments" 57 (4), April 1986, pages 519 to 528. A heterodyne arrangement and a homodyne arrangement with frequency shift for measuring velocity are shown in FIG. 1 of this article and are explained in the description provided therein.